How well do unborn babies hear?

Researchers said they have found stronger evidence that a fetus can hear sounds and words during the last trimester of a mother’s pregnancy.

The discovery, made by a team at the University of Helsinki, was reported in the Proceedings of the National Academy of Sciences. The researchers said women were given recordings to play for their unborn child during pregnancy. The recording contained variations of the word “tatata.” The sound was played about 25,000 times.

After the babies were born, scientists used an EEG device to confirm neural traces of the word. The study has brought new attention to neural learning in the womb.

U-T San Diego discussed the findings with Jeff Elman, a cognitive scientist who specializes in early childhood development and founding co-director of UC San Diego’s Kavli Institute for Brain and Mind. Here is an edited version of that conversation.

Q: It used to be thought that a fetus didn't actually process sounds and words. I can remember seeing people roll their eyes when a mother sang to her unborn child. This point of view has changed. Why? Is there strong evidence that a fetus can hear specific sounds and words?

A: We know directly from studies involving rats and other mammals that the part of the brain that processes sounds does process auditory stimuli. In humans, this is thought to occur by the gestational age of 27 weeks.

Q: Is it known whether a fetus is consciously aware of sound, that the noise is something specific?

A: Hard question and one we'll probably never be able to answer, depending on what you mean by "consciously aware of." But there are other ways to get at this question.

Q: How do scientists know that a fetus is actually processing sound and words?

A: There are a range of studies that show that the fetus processes specific sounds and words, and that these sounds are — after birth — recognized. For example, we know that fetuses (in utero) learn to recognize the native language of their environment, including especially, the language the mother is using. (This doesn't mean they understand the language. But if their mother speaks English, for example, they will learn to recognize this as different from other languages.)

We now that if the mother sings a specific melody or hums a particular tune, or repeats a fragment of a story over and over during pregnancy, at birth the fetus will react in a way that tells us they recognize these stimuli, compared to unfamiliar sounds. We know they also hone in on the sound of their mother's voice so that at birth, they recognize their mother's voice from voices of other people.

Q: I imagine that parents would say, "OK, so which specific sounds and words do I use? Are there certain ones that would help my unborn child?"

A: So here's where things get interesting, and where more research is needed. We know that unborn children can learn sounds that they are exposed to in the womb. But does this give the baby a leg up later in life? At this point, the evidence is that language input in general is a positive for infants in the first year or two of life. And "more is better," all things being equal. (Of course, common sense tells us that hearing a lot of screaming and shouting are probably not so good.) Think of this as "feeding the brain," in much the same way that good nutrition is good for the developing body. But are there specific sounds and words that are particularly beneficial for development? Here we are in uncharted territory. We have some ideas about what might be good, but these have yet to be tested.